In a conventional wireless communication system including a pair of transceivers communicating with one another over a wireless communication channel, there are typically a number of different data transmission rates available at which to transmit data. Generally, the higher the data rate, the more susceptible the system is to errors. Under certain circumstances, it is necessary to adapt the system to higher or lower data transmission rates based, at least in part, on environmental conditions. For example, noise on the communication channel, transceiver impairments, etc., may necessitate operation of the system at a lower data transmission rate.
The Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard addresses medium access control over a wireless local area network (WLAN). The IEEE 802.11 standard is set forth in the document IEEE Std. 802.11, entitled Supplement to IEEE Standard for Information Technology—Telecommunications and Information Exchange Between Systems—Local Metropolitan Area Networks—Specific Requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, 1999 Edition, which is incorporated herein by reference. Additional extensions relating to the 802.11 standard, including IEEE Std. 802.11a, entitled High Speed Physical Layer in the 5 GHz Band, February 2000, and IEEE Std. 802.11g, entitled Further Higher Data Rate Extension in the 2.4 GHz Band, September 2000, are also incorporated herein by reference. Rate adaptation in a wireless communication system operating in accordance with the 802.11 standard generally takes place in the transmitter at the MAC level. Known rate adaptation schemes typically rely on information acquired through acknowledgment messages received after each correctly transmitted data packet.
An acknowledgment message indicates a correctly received packet, while an absence of an acknowledgment message is generally interpreted as an error. A determination as to whether to change the data rate in the transmitter can be made in response to the number of consecutive acknowledgments that are received. After a certain number of correctly received data packets, the transmitter typically attempts to switch to a higher data transmission rate. Similarly, after a certain number of consecutive errors, the transmitter attempts to switch to a lower data transmission rate. This conventional rate-switching methodology, which is based on received acknowledgments, has the advantage of simplicity. However, it often changes the data transmission rate of the transmitter to a value that is either too high or too low, thus undesirably impacting the throughput of the system. For example, switching to a lower data rate when, in fact, a higher rate can be supported by the system results in a significant throughput degradation. The same is true when switching to a higher data rate than the system can support, thus resulting in a high packet error rate (PER), bit error rate (BER), or frame error rate (FER).
It would be desirable, therefore, to be able to obtain an accurate estimate of the signal quality of a received signal for, among other applications, controlling the data transmission rate in a wireless communication system, which addresses the above-mentioned problems exhibited in conventional wireless communication systems.